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Many, perhaps most, animal species show consistent individual differences in behaviors—often referred to as “animal personalities” or “behavioral types”. While such personality differences between individuals are well-documented, biologists are only beginning to explore the fitness consequences of these behavioral types, especially in the field and across multiple life stages. In this study, three researchers from Michigan State University (Nicholas Ballew, Gary Mittelbach, and Kim Scribner) examined the effects of boldness in largemouth bass (Micropterus salmoides) on juvenile survival and adult reproductive success in a series of experiments conducted at the Kellogg Biological Station's experimental pond facility in southwest Michigan, USA (see photo).

Four experiments conducted in these large outdoor ponds over multiple years produced two important results. First, juvenile bass scoring high in boldness had much lower survival than shy bass. Second, adult male (but not female) bass that were bold had higher reproductive success than their shyer counterparts. Additionally, measures of boldness were highly consistent in individuals measured over multiple years and boldness was significantly heritable as judged by parent-offspring regression. Taken together, these results demonstrate for one of the first times under semi-natural conditions that a heritable personality trait can affect fitness in different ways across an organism's life history. Such fitness tradeoffs provide a potential mechanism for the maintenance of personality variation within a population. These results also have important implications for the conservation and management of fishes.
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